Flow control devices, such as sliding or rotating sleeve assemblies and downhole valves, are often used in a production tubing string of a downhole completion to selectively regulate flow of fluids into and out of the production tubing string. A device called a “choke” is also often incorporated into the flow control device to throttle (i.e., “choke”) the fluid flow, and thereby provide adjustable flow metering and pressure control between the well annulus and the production tubing at the maximum possible flowing differential pressure. Flowing differential pressure is defined as the pressure difference between immediately inside and immediately outside of the choke.
Chokes are also designed to facilitate a long service life against erosion due to solid laden produced fluids. Due to the extremely high flow velocities seen through a downhole choke during operation, the standardized industry materials of choice for chokes include carbides, such as tungsten carbide, or equivalent hard ceramics or ceramic alloys that mitigate erosion. Although adequate for erosion resistance, such materials are brittle and prone cracking or shattering due to elevated vibrations and high flowing differential pressures often experienced during injection operations.
Typical chokes used in conjunction with downhole flow control devices have a cylindrical geometry designed to fit within the confines of the generally round flow control devices. Cylindrical chokes typically have symmetrical flow performance due to equal and opposite spaced orifices that operate to cancel the energy of the flow streams coming in or going out of the choke. The oppositely spaced orifices in the cylindrical chokes also mitigate erosion in the interior of the flow control device caused by impinging jets, vortices, and turbulent flow, and thereby generally act as a shield.
While the aforementioned features are admirable, cylindrical chokes inherently suffer from circumferential stresses (also called hoop stresses) generated in the cross-section of the choke. Such circumferential stresses are due to the differential pressure of fluid acting from the inner radial fiber to the outer radial fiber, and thereby risking fracture of the erosion-resistant material at peak stress. Accordingly, one the limiting factor for cylindrical choke performance is the maximum allowable hoop stress by nature of the cylindrical geometry, which in turn is dictated by the pressure drop or flowing differential achieved before the maximum stress is reached. Another limitation of cylindrical chokes is that they have pre-defined flow characteristics by way of the in-built orifice design, which are often not replaceable externally without disassembly of the flow control device.